PhD projects are offered and supported by any one of the institutes in the Research School. Supervising scientists not affiliated with one of the partner universities share the supervision with a faculty member. The thesis will be written in English; students are expected to publish at least two papers in refereed journals during their PhD period.
A Thesis Advisory Committee (TAC), to be named at the beginning of the thesis work, guides the student through the preparation period and monitors her/his work. The TAC consists of the thesis supervisor and one or two other senior staff members of the institutes involved in the research school. At least one of the members must be a regular professor at the university at which the student is inscribed.
The following list gives an overview of the variety of research topics, but it is not complete. Some projects may already be taken, and others not mentioned will be available.
Solar-like oscillations are caused by sound waves, excited by turbulent convection, that are trapped within a star. The purpose of helioseismology is to observe and interpret solar oscillations to learn about the internal structure and dynamics of the Sun. The data from the MDI telescope aboard the ESA/NASA SOHO satellite have yielded numerous exciting results. In particular, the validity of the basic standard model of stellar structure has been confirmed, and rotation has been mapped as a function of depth and latitude in the convection zone. Current studies focus on new techniques of local helioseismology to produce three-dimensional maps of the subphotospheric flows and temperature inhomogeneities. Possible thesis topics include the development and implementation of diagnostics tools of local helioseismology to probe the internal structure of sunspots and the dynamics of convective flows. Below is a map of horizontal flows around a sunspot, 1 Mm beneath the solar surface.
Helioseismology is a growing field of research, with several missions planned for the future (HMI, Solar Orbiter). In addition, solar-like pulsations have recently been detected on other stars than the Sun from ground-based observatories. It is hoped that high-precision stellar seismology will become a reality with the ESA space mission COROT.
[top]The source of the solar magnetic field is thought to be a self-excited hydromagnetic dynamo process operating near the base of the convection zone. The details of the dynamo mechanism are still poorly understood. Lacking direct observations of the magnetic field in the solar interior, one can obtain indirect evidence by comparing surface observations with theoretical studies of the magnetic field dynamics in the convection zone. Large-scale numerical simulations as well as simplified models are used to investigate the formation of magnetic structures, their rise through the convection zone, their interaction, instability and fragmentation, their emergence at the solar surface and their development thereafter. Such studies can be extended and modified in order to investigate similar processes in other stars with outer convection zones.
The large-scale magnetic fields of the Earth and Sun are generally ascribed to a hydromagnetic dynamo acting in the interior of these celestial bodies. In both cases there is considerable variation in the generated field. The cyclic behaviour of solar activity varies both in strength and duration, with extended periods of much reduced magnetic activity. The dipole moment of the geomagnetic field fluctuates considerably, and most interesting are fast reversals of the dipole at irregular intervals. This variablity shall be investigated by considering stochastically and deterministically varing elements of the dynamo process. The simulated results shall be statistically compared with the observed quantities to possibly reveal the causes of the variability and of the dynamo process itself.
Literature:
Schmitt, Ferriz-Mas and Schüssler, A&A, 311, L1, 1996
Ossendrijver, Hoyng and Schmitt, A&A, 313, 938, 1996
Schmitt, Ossendrijver and Hoyng, PEPI, 125, 119, 2001
The magnetic field is the basic quantity that causes all the various active phenomena on the Sun (flares, mass ejections, sunspots, the hot corona, etc.) The Group Ground based solar observations (GBSO) specializes in state of the art measurements of the Sun's magnetic fields and is thus at the heart of solar physics. Techniques including the Zeeman effect in spectral lines are used to determine the 3-D structure of the magnetic field vector, the velocity field, temperature, etc. An advanced inversion code is used to derive these images and extract the huge amount of information on the structure of the solar atmosphere and its magnetic field from the observed high resolution spectra. The results are ideally suited to verify and improve theoretic models of all kinds of solar phenomena. The GBSO group offers manifold possibilities to work between theory and data analysis. Your work as a PhD student will benefit from
- state of the art instrumentation for obtaining data (eg. the MPS/IAC Tenerife Infrared Polarimeter II),
- the possibility to carry out observations with one of the worlds leading solar telescopes in exciting locations (eg. the Vacuum Tower Telescope on Tenerife or the Swedisch Solar Telescope on La Palma),
- the access to data from space-born telescopes like Solar-B or SOHO,
- the presence of high quality analysis software for spectropolarimetric data and
- the close connection with theoretic modeling of solar observables.
The Vacuum Tower Telescope on Tenerife, harboring our Infrared Polarimeter
Polarimetric signal of a magnetic sensitive spectral line: The Zeeman effect increases the splitting of the sublevels of an atomic transition. The magnetic field direction can be inferred by analyzing the linear and circular polarization state of the spectral line (Stokes parameters: I, Q, U and V).
The interaction of magnetic fields with convective flows is a key process for understanding the magnetic activity of the Sun. It leads to intense concentrations of magnetic flux, to the formation of spatial patterns in the distribution of magnetic flux, to the heating of the chromosphere and corona, and to local dynamo action. Realistic numerical simulations on parallel computers are carried out to study the basic physical of magneto-convection in concert with results from high-resolution spectroscopic observations. The simulations are carried out in 2D and 3D spatial geometry and include radiative energy transport as well as the spectroscopic diagnostics in order to compare with observational data. Possible thesis projects include the systematic study of photospheric magneto-convection as well as the extension of the physical models (radiation, ionization, diagnostics) to the conditions prevailing in the solar chromosphere and in the photospheres of other magnetically active stars.
Particle density, collision rate and ionization degree decrease strongly with height in the lower solar atmosphere, so that the application of simple one-fluid magnetohydrodynamics becomes questionable in regions around the temperature minimum and above. An exploratory study is intended to investigate under which conditions effects like ambipolar diffusion and the Hall effect become relevant and when multi-fluid approaches should be used.
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The Solar magnetic field is a major factor organizing the release of plasma and wave energy from the Sun into the heliosphere. Using modern magnetographic techniques, in part under development at the MPAe, the full Solar vector magnetic field information is becoming available at higher resolution than ever. Since direct measurements of the solar magnetic fields are restricted to a thin layer close to the Solar surface the fields have to be extrapolated to the Solar atmosphere (Figure). To understand the consequences of these fields for the heliosphere, however, one has to consider also the plasma of the Solar atmosphere in its interaction with the magnetic fields. For this purpose the PHD project aims at the development of computer models, starting with the search for appropriate equilibria. The combination of equilibrium configurations with the measured magnetic fields should provide realistic plasma models which then will be used to simulate, this way trying predict the evolution of Solar plasmas and fields. It is planned to compare the results of this modelling effort with existing observations of the SOHO spacecraft where the MPAe is heavily involved, in the future with the STEREO and other Solar missions.
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Reconnection is the main physical process of plasma heating and particle acceleration by utilizung the energy stored in magnetic fields In the "Theory and simulation of Solar system plasmas" (TSSSP) group appropriate methods are being developed to simulate the dynamics including plasmakinetic effects. The latter have to be taken into account since in the collisionless and complex space plasmas direct interaction between particles are rare and collective effects therefore prevail. The resulting physical effects are highly nonlinear. They can be best described by numerical simulation techniques. In the TSSSP group at MPAe different types of codes have been developed which can be applied using powerfull parallel computing facilities. One of the PHD projects in this direction is to investigate the consequences of three-dimensional reconnection (Figure) for the dynamics of the Solar atmosphere, particle acceleration into the Solar wind and radiation. A special role which has to be investigated plays the magnetic helicity, a remotely measurable quantity, its creation, evolution, transport since it might enable us to predict Solar eruptions and their consequences for the space wheather at Earth.
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The transition region of the Sun is a network of highly dynamic magnetic loops. At any one time there are tens of thousands of microflares and explosive events occurring throughout the region. Each one lasts 1-4 min and is about 1000 km in size. The activity is best seen in high resolution UV spectra. The movie shows a time series of SUMER spectra taken with a 10s cadence.
There is a strong belief, supported by both the event structure (Innes et al., Nature, 386, 811, 1997) and MHD models, that the events are powered by magnetic reconnection. Recently, new facts and ideas have emerged on the energetics of these events. These can be tested with data we have from series of SUMER observations. The Thesis would be an analysis of the SUMER spectra, and subsequent modeling of the event flow and energetics.
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Coronal downflows are clouds or structures that fall from a distance of up to 5 solar radii down towards the Sun. They are not, as one might imagine, pulled primarily by the Sun's gravity but by magnetic forces. Downflows are occasionally seen after coronal mass ejection, but the majority are associated with magnetic boundaries in the slow solar wind.
The properties and structures in the downflows can lead to important insight on magnetic field structure in the corona, and the associated build-up and release of magnetic stress far above the solar surface. They appear to be newly formed magnetic loops collapsing down to the surface of the Sun. At the same time releasing magnetic flux into interplanetary space. A careful look at the movie reveals simultaneous in- and out-flowing plasma from a point near the middle of the images.
The shape of the wave fronts, the acceration rates, the background and event brightness will be combined with models of the coronal magnetic field to probe the dynamics of downflows.
A SOHO hotshot on downflow is at http://sohowww.estec.esa.nl/hotshots/2001_11_20
[top]Mini-CMEs (Coronal Mass Ejections) are supergranule sized eruptions that are seen in the lower corona throughout the quiet Sun. Two typical events, seen in sequences of STEREO 171 images are shown in the movies (field-of-view 200"x200").
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| Gif Animation (8 MB) | Gif Animation (8 MB) |
These types of eruptions were suggested as a main driver for coronal heating in 1998, and are a recent discovery of the STEREO mission. The current estimate is that at any time, one tenth of the solar surface is effected by mini-CME events. Thus they could well be a major contributor to coronal heating in the quiet Sun. The aim of this project is to find out their actual contribution.
For a PhD starting in January 2009, the timing is perfect because at the end of 2008, the Solar Dynamics Observatory (SDO) will be launched. With its set of EUV filters and high cadence images, these types of events will be captured in much better detail than with STEREO. In addition SDO observations of the photosphere will provide a wealth of information on the trigger mechanism.
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The
solar VUV spectrum from 50 nm to 160 nm recorded by SUMER
It was the combined development of spectroscopy and atomic physics that led, at the end of the thirties of last century, to the discovery of a hot (over one million K) corona above the cool (5780 K) solar photosphere. Since then, the development of the available instrumentation and atomic physics calculations have provided an increasing sophisticated and powerful tool for the study of the solar and stellar coronae.
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The low density (about 109 electrons cm-3), optically thin coronal plasmas emit a spectrum dominated by emission lines (generally due to exitation by electron collisions and subsequent spontaneous decay) and continuum. This radiation is function of the thermodynamic state of the emitting source (i.e., density and kinethic temperature of electrons and element abundances). Thus, the knowledge of the atomic processes leading to the formation of lines and continuum coupled to the measurement of the emitted radiation allows the characterization of the emitting source. Spectroscopy, in particular, besides isolating specific emission lines, allows the measurements of plasma motions on scales larger (bulk motions leading to Doppler shift of the entire line) and smaller (modification of the line profile) than the spatial resolution, providing information on the dynamics and mass transport in the atmosphere. Moreover, being the coronal plasma forced to move along the magnetic field lines, the radiance and velocity patterns trace the magnetic field well above the photosphere, in regions where cannot be measured directly. The Figure on the side shows an example of velocity maps obtained by SUMER. In this case the target was a large sunspot, but such studies can be performed on any other region of the Sun. |
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The coronal emission falls almost entirely in the vacuum ultraviolet (VUV: 10 to 200 nm). Thus, the study of solar and stellar coronae requires space instrumentation. The VUV group at MPS is very active on this research topic. It has built and operates the SUMER spectrograph aboard the SOHO spacecraft and is involved in several other important present (Stereo) and future (Solar Orbiter) solar space missions.
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The solar magnetic field couples the solar interior with the photosphere and corona where it drives heating processes and eruptive phenomena. In the corona the magnetic energy is quasi-statically built up until it exceeds by far the energy stored in a potential magnetic configuration. This excess energy is intermittently released in parts by large eruptive phenomena, e.g. coronal mass ejections, flares and eruptive prominences, but also through small ones, such as explosive events and nano- and micro flares which are probably central for heating the solar corona. Knowledge regarding the coronal magnetic field therefore plays a key role for obtaining a better understanding of these phenomena. Most measurements of the magnetic field vector are restricted to the photosphere, so that the magnetic field needs to be extrapolated from there into the corona. High resolution vector magnetograms are available from ground based (SFT, SOLIS) and space born instruments (Hinode, from 2009 on SDO). Codes for modelling the chromospheric and coronal magnetic field have been developed at the MPS.
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Coronal holes are regions with a strongly reduced emissivity in coronal lines, while the emissivity in cooler transition region radiation is only slightly reduced compared with the quiet Sun. Coronal holes are characterized by the dominance of one magnetic field polarity on an extended surface region which feeds open magnetic flux into the heliosphere on large scales. On small scales, however, also closed magnetic loops may exist of in coronal hole regions. The average length and height of these loops is much smaller than in the normal quiet Sun regions. The plasma stored on these low level loops is responsible for the cool transition region radiation out of coronal holes while the the absence of long coronal loops explains the absence of EUV ad X-ray emissions. An open question is why and how do coronal holes occur and vanish? Current theories suggests that coronal holes are generated prefrentially close to the boundary of decaying active regions. Magnetic field line reconnection is assumed to play an important role within this process. It is also unclear, how a coronal hole finally vanishes and is converted into a normal quiet Sun region. The aim of this project is to study the temporal evolution of coronal holes and the nearby regions. Photospheric magnetic field data are currently available from ground based observations and space missions (SOHO, Hinode and from 2009 with SDO). With these means, the magnetic field topology should be analyzed be in closed connection with the plasma radiation observed with the two STEREO spacecraft and the coronal plasma flow via SOHO/SUMER Doppler maps.
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The two STEREO-spacecraft observe the Sun from two vantage points in space. Coronal EUV-images from these two viewpoints allow to derive the 3D-structure of coronal plasma loops and polar plumes. Until now the 3D reconstruction has been done mainly by classic and magnetic stereoscopy. A novel approach is to apply tomographic techniques for the 3D-reconstruction of coronal structures, which is designed in particular for the optical thin coronal plasma. Due to the high conductivity of the coronal plasma, the EUV-loops also outline the coronal magnetic field and allow to test coronal magnetic field models. The coronal modelling approaches, 3D-stereoscopy and tomography all contain measurement errors and reconstruction bias. Within this work it is planned to combine stereoscopy and magnetic modelling in order to derive the solar coronal magnetic field and plasma self-consistently from multi spacecraft observations.
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The solar magnetic field is key to understanding the physical processes in the solar atmosphere. Unfortunately, we measure the magnetic field vector routinely with high accuracy only in the photosphere with, e.g., Hinode/SOT. These measurements are extrapolated into the corona under the assumption that the field is force-free. This condition is not fulfilled in the photosphere, but is in the chromosphere and corona. In order to make the observed boundary data consistent with the force-free assumption, we therefore have to apply some transformations before nonlinear force-free extrapolation codes can be legitimately applied. We developed a minimization procedure that uses the measured photospheric field vectors as input to approximate a more chromospheric like field. The procedure includes force-free consistency integrals, spatial smoothing, and an improved match to the field direction as inferred from fibrils as can be observed in, e.g., chromospheric H-Alpha images. While the combination of pre-processing and force-free modelling allows us to reasonably estimate of the chromospheric and coronal magnetic field, we do not fully understand the magnetic field structure between photosphere and chromosphere, where the field is not force-free. A significant part of the energy is stored in this region, however, and we aim for a better understanding of this relatively thin layer. Because this layer contains a finite-beta plasma a force-free magnetic field model is not appropriate here and we need to apply magneto-hydro-static models which include the plasma and magnetic field self-consistently.
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Solar variability
and climate 
The global climate of the Earth has undergone a dramatic change over the last century. The Sun is one of the major players in driving global change, through the variation of its total brightness, its spectrum and magnetic field. The main aims of the PhD projects in this field is to obtain a better understanding of the causes of the variability of solar brightness and magnetic fields, to identify and reconstruct the quantities relevant for climate change over the past centuries and millenia and to estimate the magnitude of their influence on the climate.
The figure shows the run of solar irradiance (total brightness) and global temperature over the last 150 years. Note that temperature and solar irradiance run in parallel up to approximately 1970. Since then, the Earth's atmosphere has grown significantly warmer, while the Sun's brightness has not shown such a significant trend.
There are a number of PhD topics in this field, which can be more theory oriented or more data oriented.
[top]SOHO is ESA's ongoing solar physics mission, delivering through remote-sensing observations detailed information about the plasma state of the Sun's corona. The observations indicate that coronal ions are heated through cyclotron-resonant absorption of waves at high frequencies. Existing theories, mainly based on multi-fluid and hybrid-kinetic equations, are still missing essential aspects of the underlyling basic physics. Apparently, a key role is played by pitch-angle diffusion of ions in the wave frame, in association with plateau formation in the velocity distribution functions. Evidence for this is found in the Helios in-situ solar wind observations. To understand the relevant kinetic processes and wave-particle interactions, further theoretical investigations and innovative data analysis are needed.
[top]The solar atmosphere is a prolific generator of waves and turbulence. These fluctuations propagate into the heliosphere and evolve nonlinearly in the expanding solar wind, due to interactions between solar wind streams and because of the nonuniformity of the flow. The Helios and Ulysses missions have delivered comprehensive data sets which are available to study turbulence in the three-dimensional heliosphere and over the solar cycle. The large-scale evolution and the small-scale dissipation of interplanetary magnetohydrodynamic fluctuations are not well understood. Novel data analysis and theoretical modelling are required, involving Fourier spectral analysis or the use of modern tools for time-series analysis based on concepts of chaos, fractals and intermittency.
[top]The solar wind is the continuous outflow of completely-ionized gas from the Sun's corona. The hot corona typically has (base) electron and proton temperatures of 1-2 MK and expands radially outward into interplanetary space, with the flow becoming supersonic within a few solar radii. The heating of the solar corona and the acceleration of the solar wind are outstanding problems in solar physics. The solar wind been investigated routinely over many solar activity cycles. It comes in three types: steady fast streams, unsteady slow streams and spectacular transients, the coronal mass ejections. New models are needed to understand the generation of these types of wind in the three dimensional corona. Special attention must be given to the source regions of the fast wind in the dynamic transition region of coronal holes. Time-dependent models of the unsteady slow wind, perhaps originating through reconnection in the equatorial streamer belt, still have to be developed.
[top]In-situ dust detectors on board the interplanetary spacecraft Ulysses, Galileo and Cassini have measured interstellar dust particles in the solar system. The grains originate from the Local Interstellar Cloud (LIC) outside our solar system and they act as tracers of the physical conditions in the LIC. In the inner solar system the interstellar dust stream is altered by the solar radiation pressure force, gravitational focussing and interaction of charged grains with the interplanetary magnetic field. Cosmic dust is an important player in many astrophysical processes like, for example, proto-planetary accretion discs and the formation of planetesimals. The physical processes involved in cosmic dust are of far-reaching significance. The PhD thesis deals with the interpretation of the Ulysses interstellar dust measurements and modelling the grain interaction with the heliosphere, in particular with the time-varying interplanetary magnetic field. The implications for the physical conditions of the LIC shall be assessed.
[top]Solar body tides on Mercury cause elevation changes of up to 1.5 m during one solar day. The knowledge of the planet's response to tidal forcing, expressed by the Love number h, helps to constrain the interior structure, such as the size of the core and possibly that of a solid inner core. A laser altimeter on board the space missions Messenger and Bepi Colombo will determine the surface elevation within a meter or better. A strategy for analyzing the altimeter data to get the best possible estimate of h is to be developed and must be tested by modeling with synthetic data. The implications of uncertainties in h for structural models of Mercury will be assessed.
[top]Mercury has an internal magnetic field that could be generated by a convection driven MHD-dynamo in the liquid part of its core. Possibly only a thin outer shell of the core is still liquid, which might explain the relative weakness of Mercury's field compared to other dynamo-generated planetary fields. As an alternative, the dynamo may not be self-sustained, but is assisted by currents arising from thermoelectric effects at the core-mantle boundary. In numerical simulations both self-sustained dynamos with different shell thicknesses and thermoelectrical dynamos are to be studied in order to develop an understanding for Mercury's peculiar field.
[top]Mercury's silicate mantle is only about 600 km thick and overlies a comparatively large core. Mantle convection controls the thermal evolution of the planet and is to be studied in two- and three dimensional Cartesian and spherical models. Such models will make predictions concerning the heat flow at the surface and in the core, thickness of the lithosphere, size of a solid inner core, global shrinking of the planet, topography at the core mantle boundary, and the pattern of convection. These predictions will assist the interpretation of results from the upcoming space missions to Mercury.
[top]The strength and geometry of the various planetary magnetic fields is highly variable and it is not well understood what controls them. Numerical dynamo models can successfully reproduce many observed properties, but the values of some control parameters are far from realistic. Systematic studies covering a decent range of parameters are now possible. They will be employed to derive scaling laws that link properties such as characteristic velocities, heat flow, and magnetic field strength to the control parameters. Such scaling laws, if they can be extrapolated to realistic parameter values, provide a means to explain the differences in planetary magnetic fields.
[top]The magnetic field of the Earth varies on all time scales from a few hundred years and longer. Most spectacular are sudden dipole polarity reversals which occur at irregular times, on average once every few hundred thousand years. The magnetic field is generated by dynamo processes in the convective fluid metallic outer core.
The proposed research project aims at improving our understanding of the physics of the geodynamo by making a systematic analysis of the statistical properties of the geomagnetic field. To this end the multipole components of the field will be extracted from magnetohydrodynamical simulations of the geodynamo, and subsequently compared with analytical results obtained with a new theoretical technique. The project provides an ideal environment for theoretically oriented research, but also for the application of advanced data analysis techniques.
A more detailed description is given here.
[top]Water vapour plays a crucial role in the ozone chemistry of the middle atmosphere of the Earth since it is the source gas for hydroxyl radicals. With increasing altitude in the middle atmosphere the hydroxyl catalytic cycle starts to dominate ozone depletion. The SPARC (stratospheric processes and their role in climate) water vapour assessment of the WMO-World Climate Research Programme reported a 50 to 100 % increase of water vapour in the middle atmosphere since the 1950s which can only partly be explained by anthropogenic influences like the strong increase of methane (which is oxidized to water vapour). We would like to investigate the influence of the solar ultra violet variability on the middle atmospheric water vapour and ozone (see related program: http://www.bu.edu/cawses/germanymay2005.htm). While the total solar irradiance only changes by < 0.1% over a solar cycle, the Lyman-alpha radiation, mainly responsible for water vapour photolysis, typically varies by a factor of 2. Recent theoretical work proposes atmospheric coupling mechanisms that should result in a time delayed effect of solar ultra violet variability on the middle atmospheric water vapour and ozone concentrations. The MPS is running water vapour and ozone microwave spectrometers (see: http://alomar.rocketrange.no/water-vapor.html) covering a period of nearly one solar cycle that provide unique, high quality data sets. The purpose of this PhD project is to analyze these data sets with respect to the context mentioned above and to compare the findings with the model predictions.
[top]The Herschel Space Observatory (see: http://sci.esa.int/science-e/www/area/index.cfm?fareaid=16 and http://herschel.jpl.nasa.gov/) will be launched in summer 2007 and will start its observations right away. The MPS as part of the instrument teams plays a leading role in using Herschel for solar system investigations. Specific topics covered by our guaranteed observation times concern the origin of water in the upper atmospheres of the outer planets, the Martian water cycle, the chemistry of the Martian atmosphere, and search for water in distant comets, water excitation and the D/H ratio in comets. Already in 2006 we expect to perform first science flights with SOFIA (see: http://www.sofia.usra.edu/ and http://www.irs.uni-stuttgart.de/aktuelles/). With our hardware contribution to the GREAT-instrument (see: http://www.sofia.usra.edu/Science/instruments/instruments_great.html) we intend to address similar scientific and/or complementary topics by observing solar system objects in the THz range of the electromagnetic spectrum. Depending on the qualification and interests of the applicant(s) the PhD project(s) would either focus on a planetary or cometary topic with some preference for the latter.
[top]The atmospheric circulation on Mars is driven by a complex interaction between the radiative, photochemical, and dynamical processes. General circulation models (GCM) of the atmosphere have long been a powerful tool for studying these processes on Earth, and now they are becoming increasingly important for Mars. A new state-of-the-art Martian atmosphere GCM has recently been developed in MPS within the framework of the Mars Atmosphere Observation and Modeling (MAOAM) project. We have PhD opportunities which will focus on improving physical parameterizations in the model, assimilating data from space missions, airborne and ground based measurements, and carrying out numerical simulations to understand the Martian global circulation and its variability.
This figure shows the zonal mean temperature for Ls=90 deg (left). A strong winter polar warming is observed around 60 km. Eliassen-Palm (EP) fluxes (bold red arrow lines) show the propagation trajectories of the wave action, and the thin blue lines present the EP flux divergence (right). The plot shows that the topographically generated waves originate near the surface while the thermal tides are excited in the atmosphere at various heights. In the areas of the strong EP divergence/ convergence, the waves deposit their energy and momentum into the mean circulation. The winter polar warming is strongly affected by the waves.
Equatorial diurnal variation of ozone on Mars during summer solstice calculated with the MAOAM chemistry-transport module.
Atmospheres and surfaces of planets not protected by a magnetic field like those of Mars and Venus are strongly influenced by the solar wind. For example, plasma induced atmospheric escape processes are believed to be at least partly responsible for the loss of the martian water content. The novel experimental technique of Energetic Neutral Particle (ENA) Imaging will much enhance the capabilities to study these processes by providing global images of the interaction region. The MPS is part of a large international consortium building the Neutral Particle Cameras for MarsExpress and possibly VenusExpress. A wide range of opportunities exists for students interested in atmospheric physics, plasma physics, and computational methods to participate in the preparatory modeling work and in the analysis of the first data expected from 2004 onwards.
[top]Venus is completely shrouded by a thick cloud layer that consists mainly of sulfuric acid aerosols. Its upper part contains a specie that strongly absorbs radiation in the ultraviolet spectral range and which nature had been puzzling the observers for many decades. Inhomogenities in its distribution at the cloud tops produce the UV markings observed from space. Remote sensing experiments imaging spectrometer VIRTIS and monitoring camera VMC onboard the ESA Venus Express spacecraft that orbits Venus since April 2006 collect unique data about the spectral properties and morphology of the cloud tops. These observations can shed a light on the distribution and nature of the unknown UV absorber.
This PhD project has a goal to study the distribution of the unknown absorber and its nature by
using the Venus Express observations. In particular, the work will include:
1. Analysis of the phase dependence of UV contrasts from the VMC images that bears the information
about the vertical distribution of the specie;
2. Determination of the spectral properties of the UV absorber from the VIRTIS spectroscopy;
3. Analysis of the VIRTIS spectra and VMC images to find the trace gases which distribution
correlates with that of the UV absorber and which can thus be considered precursors of the
unknown specie.
The PhD student applying for this project should have basic knowledge of the optical remote sensing of planetary atmospheres, in particular, in image processing and spectroscopy. Experience in working with the programming languages like IDL and FORTRAN is desired.
[top]The atmosphere of Venus is very thick and filled with radiatively active gases and aerosols. This results in that radiative energy transport plays a significant role in the heat balance of the atmosphere. The most remarkable manifestation of the climate forming role of radiation is the greenhouse effect responsible for very high surface temperature (~500 K). Earlier observations of Venus resulted in general description of the radiative properties of the Venus atmosphere implemented in a number of numerical models. Since April 2006 Venus Express remote sensing instruments monitore the atmosphere of the planet producing more details about the trace gases and clouds and their variability. In addition, more accurate spectral databases that include gases properties at high temperatures and pressures became available recently. The progress in both observation and laboratory fields creates necessary conditions for detailed modeling of the radiative transfer in the Venus atmosphere.
This PhD project will include computation of radiative fluxes in the Venus mesosphere and troposphere
(0-100 km), in particular
1. Updating of the optical model of the Venus atmosphere on the basis of the Venus Express observations.
2. Numerical study of the planetary balance of radiative energy, its latitude and spatial variations.
3. Numerical modeling of the vertical distribution of radiative energy deposition.
4. Investigation of the greenhouse effect, the role of different trace gases and clouds, and their variability.
The PhD project will require extensive numerical modeling of the radiative transfer in the thick Venus atmosphere including multiple scattering and absorption by gaseous bands. The applicant is expected to have experience in programming in FORTRAN and IDL languages and in working on multi-processor computing systems.
[top]Venus is completely shrouded by a thick cloud layer that consists mainly of sulfuric acid aerosols. Earlier observations tentatively showed that the altitude of the cloud top on global scale varies with latitude. Local variations are also expected to be in correlation with the UV markings. The infrared imaging spectrometer VIRTIS onboard Venus Express for the first time provides spectral maps of Venus in the region of CO2 absorption bands between 1 and 2.5 µm. Depth of these bands is proportional to the atmospheric pressure at the cloud tops and thus can be used to determine its altitude over the planet. The first attempts to use this method revealed strong variability of the cloud top altitude from ~72 km in low latitudes to 65 km at the pole. Correlation of the cloud top altitude derived from the VIRTIS spectroscopy with the images taken by Venus Monitoring Camera will provide additional insight in the morphology of the Venus upper cloud.
This PhD project has a goal to study in detail the cloud top altitude and its variations with
latitude and local solar time and to correlate the spectral observations with the VMC imaging.
In particular, the work will include:
1. Creating of the radiative transfer model to calculate the spectra of the reflected solar light;
2. Retrieving the cloud top altitude and aerosol scale height from the VIRTIS spectral measurements;
3. Correlation of the retrieved cloud top parameters with the VMC images.
The PhD student applying for this project should have basic knowledge of the optical remote sensing of planetary atmospheres, in particular, in spectroscopy and image processing. Experience in working with the programming languages like FORTRAN and IDL is desired.
[top]Venus is completely shrouded by a thick cloud layer that consists mainly of sulfuric acid aerosols with an admixture of an unknown UV absorber that produces famous markings observed on the Venus disc. Venus Monitoring Camera onboard Venus Express takes images of Venus in the UV filter centered at the wavelength of maximum contrast. Observations showed that the cloud top morphology in the middle and high latitudes is dominated by streaky features indicating significant role of horizontal quasi-laminar air flow at the cloud tops. Orientation of the cloud streaks and its variability with latitude and local time can be used to derive the wind pattern at the cloud tops, to study the role of thermal tides and Hadley cell. Moreover, the observations at the morning terminator can also give insight in the wind field on the night side of the planet.
This PhD project has a goal to study in detail the streak pattern observed by VMC and to derive
the wind field at the cloud tops. This work will support the ongoing work on the wind speed determination
from tracking the motions of the UV features. In particular, the project will include:
1. Analysis of the VMC images to derive orientation of the wind streaks;
2. Statistic analysis of the wind streaks orientation, its variations with latitude and local time;
3. Derivation of the dynamical properties at the Venus cloud tops.
The PhD student applying for this project should have basic knowledge of the image processing and fluid (atmospheric) dynamics. Experience in working with the programming languages like IDL and FORTRAN is desired.
[top]Planetary magnetospheres (the space around a planet where the planetary magnetic field dominates) are large space plasma laboratories where the whole variety of plasma processes can be studied. Especially in-situ measurements of particles, fields and waves aboard spacecraft provide new insights in processes like particle-particle- and wave-particle interactions, particle acceleration or particle precipitation in aurorae. In addition to the interaction between magnetospheric particles and moons, rings and dust the dynamics of these particles, their sources, sinks, and relative abundances could help to significantly enhance the understanding of planetary magnetospheres. The PhD candidates will work on the unique particle data sets of the Galileo and Cassini spacecraft.
Click on image for larger version
Transneptunian Objects (TNOs) in the Kuiper Belt, the cold outskirts of the planetary system beyond Neptune, are among the most primordial objects in our solar system. They represent original left-overs from the formation period of the planetary system some 4.6 billion years ago. Since discovered in 1992 only, physical properties of Kuiper Belt objects are barely studied so far, which represents a serious obstacle for the scientific understanding of the bodies and their role in the formation of the planetary system. Even size and albedo, two basic parameters of their very existence and of outstanding importance for formation and evolution scenarios of the outer solar system, are widely unknown.
In order to overcome this situation, ESA has accepted a key observing program to measure about 140 bodies for their physical parameters using the new HERSCHEL submm-Telescope. This program is the second largest to be done by this space observatory and will receive large attention by accompanying observing campaigns at ground-based facilities. The PhD thesis will be performed at the MPS and in the international environment of the HERSCHEL TNO team. It involves the understanding of the scientific objectives of this program, the preparation, reduction and analysis of the Herschel measurements that will start in 2009 and involvement in ground-based observations in support of the space project. The outcome is a thorough analysis of the Herschel results on TNOs, their meaning for TNOs per se and in the context of the planetary formation.
[top]The Microwave Instrument for the Rosetta Orbiter (http://www.mps.mpg.de/de/projekte/rosetta/miro/#contribution) is the first radio telescope flown on a "deep space" mission. Since its launch in March 2004, MIRO has already observed a comet and (during the Rosetta Earth fly by in March 2005) provided valuable data about the composition of Earth upper atmosphere. On July 4 of this year (2005) MIRO will observe the increase in water production of Comet 9P/Tempel 1 after the Deep Impact spacecraft has crashed on the comet. MIRO operates in the millimeter and submm domain of the electromagnetic spectrum and observes water and its isotopes, carbon monoxide, ammonia and methanol. The extremely high spectral resolution of 10-7 enables the instrument to exactly determine the spectral line shapes of these molecules and measure their Doppler shifts. Since the distance of the Rosetta spacecraft from the cometary nucleus is so small, MIRO will measure spectral line shapes never seen before and provide completely new clues about processes happening in the inner coma of a comet. MIRO will for instance identify active areas on the cometary nucleus and exactly determine their molecular dependent outgassing rate (via the line strengths) and the velocity distribution (via Doppler-profile/shift). Furthermore MIRO will provide temperature profiles within the inner coma (excitation state of methanol lines) and information about the hydrodynamic of gas jets. The goal of this PhD project is to simulate the molecular spectra we expect to observe with MIRO as a function of the distance from and view on the comet and vice versa to investigate how exactly the input parameters of the simulation can be retrieved from the spectra.
[top]Spacecraft missions, advanced ground-based observation techniques and state-of-the-art numerical models are used to investigate the physical, geological and mineralogical properties as well as the orbital characteristics of asteroids. Albeit some main-belt and Near-Earth-Asteroids have been already visited by spacecrafts our current knowledge of these bodies is far from being complete since the diversity within this group of objects is large. At MPS asteroids are studied in three major fields: 1) by ground-based observations which are used to explore the general physical parameters and the overall mineralogy of asteroid surfaces, 2) by studying new mission concepts to visit Near-Earth-Asteroids (e.g., Marco Polo, ASTEX) and 3) by participation in NASA’s DAWN mission that will orbit the main belt asteroids 4 Vesta and 1 Ceres. Students will obtain an outstanding opportunity to become familiar with ground-based as well as in-flight observations of asteroids.
[top]The development of a model describing cometary activity the release of gas and dust when a cometary nucleus is heated by the sun is a challenging task. Activity is driven by the sublimation of ice but this ice is not visible on the surface. It is covered by inert refractory material that is much hotter then the sublimation temperature of the ice. Recent space missions confirmed this picture. Active areas could not be localized. A very small thermal inertia and hence small heat conductivity was observed. Cometary activity removes material from the nucleus surface. The refractory layer has to be thin enough that it does not quench the sublimation and hence activity but thick enough to hide the ice. A model of cometary activity has to describe how this delicate balance can be maintained. Thus, a physically reasonable microphysical model of mass and energy transfer inside a highly porous ice/dust medium has to be developed investigating possible scenarios of dust release and interaction with an accelerating gas flow.
We have developed a full 3D time dependent numerical model of heat transfer in a porous matrix. This model allows us to simulate all major processes of heat transfer via conduction, gas convection, and radiation absorption. We can also take into consideration time transformation of a simulated region, e.g., surface erosion due to gas sublimation and formation of dry dust layers on the surface. In the frame of this microphysical model we investigate the accumulation of dust on a cometary surface and the condition of a particle release. These calculations should be the starting point for a more realistic model of cometary activity.
The Rosetta mission will rendezvous with a cometary nucleus. One of its major scientific goals is to disclose the physics of cometary activity. The proposed PhD thesis should provide a realistic tool for the interpretation of the planned observations.
[top]On route to its main target, periodic comet 67P/Churyumov-Gerasimenko, Rosetta, ESA's mission to the origins of the solar system, visits two asteroids of the main asteroid belt: 2867 Steins visited already in 2008 and 21 Lutetia in 2010. Camera imaging is a key element of the scientific measurements performed during the flybys. Important results expected from the flybys are models for the detailed shape of the asteroid and for surface terrains on the asteroids. These three-dimensional models have to be determined from two-dimensional images obtained of the body silhouette and from different aspect angles, respectively. The two theses (one each on the shape model and on the terrain model) shall apply existing approaches and also new techniques to derive qualified results on important physical parameters like body volume and density, rotation properties, surface topography, light scattering properties of the surface etc. The developed modeling approaches can also be applied to existing datasets of other solar system bodies and to forthcoming measurements of the Rosetta spacecraft at the main mission target. For questions and supervision of the work feel free to contact Drs. Holger Sierks and Hermann Boehnhardt at MPS Katlenburg-Lindau.
[top]The Max-Planck-Institut für Sonnensystemforschung is one of the world's leaders in solar instrumentation. Current projects are contributions to the SECCHI suite of optical instruments to fly on the two STEREO spacecraft (aim: stereoscopy of the Sun), an infrared polarimeter for the solar observatory on Tenerife, a mirror-coronagraph and H-alpha telescope in Argentina, among others.
The Institute is also leading a consortium to build a balloon-borne telescope to obtain the highest resolution images ever taken of the Sun and is playing a leading role in the "Solar Orbiter", the next solar mission of the European Space Agency (aim: explore the Sun's poles and go closer to the Sun than any other mission before).
There are numerous opportunities for PhD theses by experimental physicists interested in developing, designing, building, calibrating, testing and/or employing magnetographs, visible and UV imagers, polarimeters, visible and EUV spectrometers and coronagraphs.
[top]The COSAC experiment on Philae, the Rosetta Lander, is a combination of a gas-chromatograph and a mass-spectrometer. The spacecraft was launched in March 2003 and is now on its way to comet 67P/Churyumov-Gerasimenko. COSAC will offer the first chance in history to investigate the composition of the volatile fraction of a cometary nucleus in-situ. Judging from artificially produced cometary ice analogues it is hoped to find molecules of possible biological relevance in the cometary material.
In order to interpret the data which will be gathered in 2014, experimental work based on the knowledge of earth-based measurements and theoretical modelling is required. For this work a flight identical instrument is operated at the MPS. The PhD project would include characterisation of samples using the aforementioned instrument with regard to chemical composition, chiral distribution, and possibly isotopic composition. Additionally evaluation routines for the identification of unknown samples may be developed.
The work will be carried out in an international team of mainly French and German members. It will be a combination of practical and theoretical tasks of physical, chemical, and engineering nature. The results of the work will help in selecting the optimum operating parameters for the scientific measurement sequences on the comet and aid the successful interpretation of the results of the mission.
The image shows the flight hardware of COSAC shortly after integration on the spacecraft.
MPS has more than 20 years experience in the development of Chirp Transform Spectrometers (CTS). These spectrometers have been used in ground-based, air- and spaceborne millimeter- and submillimetre wave heterodyne experiments. The Chirp Transform (CT) is equivalent to the Fourier Transform. The algorithm describes how to implement a Fourier Transform using linear dispersive pulses and their matched filters. CTSes have several advantages compared to other spectrometer concepts leading to superior measurement accuracy. At the same time a CTS can be designed in a way that mass and power consumption is very small compared to other techniques - an important advantage for space borne applications. The key components in presently used CTSes are the so called surface acoustic wave (SAW) dispersive delay lines (DDLs). The SAW-DDLs are passive signal processing devices. The signal processing capability is achieved by the interaction of surface acoustic waves with sub-µm structures on a piezoelectric substrate. The purpose of this PhD project is to investigate how the maximum CTS- bandwidth of presently 400 MHz can be extended and to find out the physical and technical limits. The project phase I will focus on the design, fabrication and test of new ultra-high time-bandwidth-product DDLs, based on classical materials like LiNbO3, phase II on the investigation of new materials (like for instance TiO2) for this purpose and phase III on testing these new devices in a newly designed CTS. The project will be done in collaboration with PTB ( http://www.ptb.de/index_en.html) and it is assumed that the PhD student will perform his studies to about 50 % of his time there. PTB provides modern high resolution electron beam lithography, metallization and dry etching techniques and is experienced in the production of high frequency SAW, resp. single electron tunneling devices (http://www.ptb.de/en/org/2/25/253/verweis/_sing_electr_transp.htm).
Water vapour spectrum at 22 GHz measured with CTS and retrieved vertical profile of water vapour.
The large scale magnetic fields of astrophysical objects such as planets are thought to be generated by the hydromagnetic dynamo process. In this process the motion of an electrically conducting fluid in the presence of a magnetic field generates an electrical current which produces the field. This dynamo process is a threshold process. No field is generated unless the vigour of the fluid motion exceeds a critical level. In recent years much progress has been made understanding the very complex processes in dynamos using numerical simulations. These numerical models typically assume that the dynamo process alone is capable of sustaining the magnetic field. However, there are examples where an external field plays an important role: the Galilean satellites are imbedded in the large Jovian magnetic field, planet like Mercury is surrounded by a significant magnetospheric field due to the planet's interaction with the solar wind. In the presence of an external, ambient magnetic field the condition on the dynamo's fluid motion to exceed a critical level is relaxed. Fluid motions having the usual regenerative character can distort and amplify the ambient field to produce an internal, dynamo-like magnetic field for all amplitudes of the fluid motion. Numerical experiments are necessary to further understand such magneto-convective dynamos. The suggested dissertation topic emphasizes such experiments with particular attention paid to planet Mercury. A numerical code to perform the suggested experiments is already available.
[top]CLUSTER, that is Europe's ongoing four spacecraft mission to the Earth magnetosphere. The magnetosheath, that is the subsonic transition region between the bow shock in front of the Earth and the magnetopause as the boundary between solar wind and magnetospheric plasma, is characterised by large amplitude plasma waves of different type and origin. Different wave modes may be described by their respective eigenvectors, and each set of observations such as magnetic field, plasma velocity and density can be decomposed into its associated eigenvectors. Such a mode filter or mode projection approach will lead to a new look at the plasma waves of the magnetosheath. Applicants interested in theoretical plasma physics and data evaluation techniques are particularly welcome.
[top]ROSETTA, that is Europe's ambitious mission to land on and orbit comet 67P/Churyumov-Gerasimenko. With a launch in 2004 the ROSETTA spacecraft will need 8 years to reach its aims - comet 67P/Churyumov-Gerasimenko. Equipped with a modern plasma and fields instrument ROSETTA will be able to unravel some of the open question of the plasma interaction between the solar wind and comets. Using existing numerical simulation codes the interaction should be simulated to prepare future spacecraft operations and experimental strategies. A close cooperation with the experimenters is required. Applicants interested in theoretical plasma physics and numerical simulations as well as interest in spacecraft operations are particularly welcome.
During the last few years the astronomical observation techniques have become more and more sophisticated leading to precise detection methods of planets orbiting stars other than our sun. Presently more than 170 extrasolar planets are known. Compared to the situation in the solar system extrasolar planets may have quite different properties, different orbits and completely new types of interaction with the stellar wind. The interaction of extrasolar planets with the corresponding particle flow from their host stars (stellar wind) shall be modeled by analytical and numerical methods. Intention of the modeling is the structure of extrasolar magnetospheres and mechanisms of generation of electromagnetic radiation in these magnetospheres. Of special interest is the radio emission of extrasolar planets as a new giant radio array called LOFAR will be available in near future. Applicants interested in modeling and numerical work are particularly welcome.
[top]Modern observations of solar system bodies can reveal information concerning the composition, density and size distribution of the regolith covering planetary, lunar, asteroidal and cometary surfaces. The flyby of ESA's ROSETTA spacecraft by the asteroid Steins in September 2008 shall be used for the determination of mechanical regolith properties, such as the angle of repose, maximum slope angles and the occurrence of avalanches on Steins. The successful participant will work at the MPS within the OSIRIS team; supporting laboratory experiments on regolith behavior under low-gravity conditions shall be carried out in collaboration with the TU Braunschweig team so that the data analysis from the Steins flyby can be based on a strong physical background.
[top]We have recently submitted a proposal for a testflight of the new private "New Shepard" rocket of the US company Blue Origin. If accepted, we will be able to send a sizeable experiment onto a 3-minute weightlessness parabola, with which we intend to study the low-velocity collision behavior of small dust particles. The PhD student will be concerned with the development and testing of the flight hardware (supported by a Master student of the TU Braunschweig; delivery date of the hardware is 15 Nov 2010), the programming of the flight software, attendance during the flight, post-flight data analysis and modeling of the experiment. We also encourage additional microgravity experiments in the Bremen drop tower. The results of the experiment will greatly enhance our knowledge on the collisional evolution of protoplanetary dust.
[top]Our knowledge about physical properties of stars almost exclusively comes from spectroscopy, and spectroscopic absorption lines carry enormous information about stellar surface structure - e.g. spots, velocities and magnetic fields. Absorption lines are densely packed in cool stars (like the Sun) blurring the information contained in the line shape. Techniques to reconstruct such information are being widely used nowadays but are still in their infancy. One goal is to improve techniques reconstructing stellar absorption profiles, and apply them to high quality astronomical data - more and more of which become available thanks to the growing number of telescopes providing high resolution spectra. On the other hand, individual spectral lines are compared to theoretical models of stellar atmospheres. Improvements of such models can, e.g., include the calculation of magnetic field signatures in rotating stars.
Successful reconstruction of line broadening in a stellar triple system.
The most frequent stars in our galaxy are cool stars of spectral type M. Their faintness makes detailed investigation difficult, and surprisingly few is known about their atmospheric structure. At such low temperatures, molecules dominate the visual and infrared spectra and become the most significant tracers of stellar atmospheres. Molecular bands, however, are much more complex than atomic lines and their fundamental constants are difficult to measure in the laboratory or to calculate ab-initio. On the other hand, molecular bands are very temperature sensitive and it is possible to measure fundamental molecular constants from astrophysical observations. Spectroscopic data for such measurements has become available through 10m class telescopes providing high quality data even for very faint stars. Molecular constants, once measured, will improve theoretical calculations of stellar atmospheres, and allow an accurate characterization of very cool M-star atmospheres.
[top]Several magnetohydrodynamics experiments are currently in operation or under construction (see the figure), which are intended to reproduce on a laboratory scale the mechanisms relevant to dynamo action in planetary cores or stars. All these experiments face the question as to what can be learnt from them about the geophysical or astrophysical problem they are supposed to explore. Numerical simulations are necessary in order to identify the characteristics common to experimental dynamos and dynamos occuring in nature. A possible topic of a PhD thesis is the investigation of the influence of turbulent fluid motion on dynamo action.
The basic problem is delineated in the figure. The earth consists approximately of three layers: the inner core (IC), the outer core, and the mantle. Outer core and mantle meet at the core mantle boundary (CMB). The outer core, i.e. the region inbetween rIC and rCMB, is liquid. The motion of this liquid (mostly iron) is believed to be at the origin of the earth's magnetic field. The earth revolves once a day about the axis joining geographic north and south poles, and this axis itself precesses about the normal to the ecliptic which forms an angle of 23.5o with the diurnal rotation axis. The problem is to determine the fluid flow inside the outer core driven by the precessional motion of the solid boundaries. This flow could participate in the generation of the Earth's magnetic field. Another problem is the determination of the long term evolution of the earth-moon-sun system if the dissipation due to precession is taken into account.
The fluid motion driven by precession is also relevant for satellite dynamics, for instance when a manoever needs to be planned in which the spin axis of a spin stabilized satellite containing liquid fuel is reoriented.
Turbulent convection is an ubiquitous phenomenon in geophysics and astrophysics, frequently in a rotating fluid or under the influence of a magnetic field. Even the simplest case of Rayleigh-Benard convection is not fully understood. The focus is at present on coherent large scale structures which persist in the presence of small scale turbulent fluctuations.
